Planar magnetron



Oct. 12, 1965 .1. FORMAN PLANAR MAGNETRON Filed oct. 2s, 1961 United States Patent O 3,211,948 IPLANAR MAGNETRON .Ian Forman, 10548 Eastlrorne Ave., Los Angeles, Calif. Filed Oct. 23, 1961, Ser. No. 146,903 3 Claims. (Cl. 31E-39.71)

This invention relates to magnetron tubes and, more particularly, is concerned with a magnetron tube having planar electrodes.

The conventional split anode magnetron tube consists of at least a pair of coaxial cylindrical electrodes surrounding a central electron emitter with a magnetic eld aligned with the common axis of the electrodes. The central electrode is heated and operates as the cathode for emitting electrons into the space between the electrodes. The cylindrical electrodes act as anodes and areV generally maintained at a positive potential with respect to the cathode. The Vanodes may be split into pairs or multiples of pairs of elements, which are arcuate in shape,

The present invention is directed to an improved magnetron tube construction generally of the split anode type, but which is more rugged and easier to manufacture and which is especially suitable for ceramic tube construction techniques. Furthermore, the magnetron of the present invention may be constructed to operate in an inverted fashion, namely, with a pair of electron emitting cathodes and a single anode.

In brief, the magnetron tube structure of the present invention comprises a pair of dat or planar electrodes mounted within a vacuum envelope `and spaced in parallel relationship to each other. An elongated or rodshaped electrode is positioned between the two planar electrodes. Magnetic means is provided for applying a magnetic field having the lines of force extending between the planar electrodes and parallel to the flat surfaces thereof. In one form of the invention, the elongated electrode acts as an electron emission source, a heater being positioned within the electrode to heat the electrode to an electron emissive temperature. In this conguration, the two planar electrodes act as anodes. The tube may be arranged in alternative fashion with the two planar electrodes providing opposing electron emissive surfaces and the elongated electrode acting as the anode. Heat may be applied to the planar electrodes in a number of ways to bring the planar electrodes up to an electron emissive temperature.

For a more complete understanding of the invention, reference should be made to the accompanying drawings, wherein:

FIGURE l is a sectional View of one embodiment of the invention including a schematic showing of associated circuitry;

FIGURE 2 is a cross sectional view taken substantially on the line 2-2 of FIGURE 1 and showing the magnet structure for applying the magnetic field to the magnetron;

FIGURE 3 is a sectional view of an alternative construction of the tube of the present invention; and

FIGURE 4 is a top view of the tube embodiment of FIGURE 3 with the addition of the magnetic poles for applying the magnetic tield to the magnetron tube.

Referring to the invention as illustrated in FIGURES 1 and 2, the numeral 10 indicates generally the envelope of the tube, the interior of which is provided with a high vacuum. The cathode of the tube comprises an elongated hollow rod-shaped cathode sleeve 12 conventionally made of nickel and coated with an electron ernissive material. The cathode sleeve may be Supported, for ex ample, by projecting it `from the wall forming the envelope into the center region of the tube. The rod ICC shaped cathode sleeve 12 is provided with a conventional cathode heater extending into the hollow interior, the leads 13 to the heater being brought out through the tube envelope for connection to a heater current source (not shown).

Equally spaced on either side of the cathode sleeve 12 are a pair of planar anodes 14 and 16 of nonmagnetic material such as molybdenum, tantalum, or stainless steel. These electrodes, as shown in FIGURE 2, may be rectangular in shape. They are arranged with the broad surfaces substantially parallel to each other and extend parallel to the longitudinal axis of the cathode sleeve 12.

Planar electrode 14 is supported by four nonmagnetic metallic rods 18 extending through and supported by one end of the envelope 10. Any of the rods 13 may be used to provide an external electrical connection to the planar electrode 14. Similarly, the planar anode 16 is supported by four nonmagnetic metallic rods 20 projecting through and supported by the opposite end of the tube envelope 10. Any of the rods 20 provides an external electrical connection to the planar anode 16.

By Way of example only, the anodes may be made of two rectangular plates of stainless steel M2 long and Mr wide and positioned about Ms on either side of the cathode. The cathode sleeve may be .045 inch in diameter. A tube of the above dimensions when placed in a D.C. magnetic field extending parallel to the plane of the anodes and preferably 45 to the longitudinal axis of the cathode sleeve may be operated as an oscillator. As shown in FIGURE 2, a magnet structure indicated generally at 22, which may be either a permanent magnet or an electromagnet, is positioned with the pole face 24 and 26 positioned on the outside of the envelope 10. The magnetic held extending between the pole faces is substantially parallel to and passes between the planar anodes 14 and 16. The angle between the magnetic eld and the longitudinal axis of the cathode may be varied by changing the position of the poles as desired, but preferably is at y45" to the cathode axis.

The oscillator circuit is shown schematically in FIG- URE 1 in which a center tapped inductance 23 is connected at each end respectively to the `anodes 14 and 16. The center tap of the inductance 28 is connected to the cathode 12. A potential may be applied between the cathode and anodes by means of a battery 30. Under these conditions, the circuit may be made to oscillate as a conventional split anode high frequency oscillator. An output signal is derived across an output winding 34 which is inductively coupled to the inductance coil 28.

In copending application Serial No. 807,590, now Patent No. 3,029,397, tiled Apr. 20, 1959 in the name of the inventor of the present invention., there is described a low frequency oscillator circuit utilizing a split anode type of magnetron. The tube described above in connection with FIGURES 1 and 2 may be utilized in such a circuit by making the inductance 23 a high inductance with a low Q, such as an iron core inductance, and connecting the cathode directly to the center tap with no applied potential between the cathode and the anodes.

Among the advantages of a planar magnetron tube, is that it oan be kadapted to a structural form o-f extreme simplicity and great ruggedness. Moreover, it may be operated in an inverted manner, that is, with the center electrode operating as the anodeand the two planar electrodes operating as cathodes. This latter arrangement has the yadvantage that a number of heating methods may be readily utilized and is adaptable to known ceramic tube manufacturing techniques.

Referring to the: form of the invention as shown in FIGURES 3 and 4, the tube includes a pair of cylindrical walls 33 and 39, preferably made of ceramic material. Metallic cup-shaped members 40 and 42, preferably of titanium, form the end walls of the tube envelope and constitute the two planar cathodes of the tube. The cupmember 40 includes an outer flanged portion 44 which is secured in vacuum-tight relation to the cylindrical wall 3S. The recessed portion of the cup-shaped member projects inwardly and provides a planar surface 46. The cup-shaped end member 40 serves as one of the planar electrodes. Similarly, the other end member 42 is provided with a flanged portion 48 which is secured in Vacnum-tight relation to the cylindrical wall 39 and has a recessed portion forming a planar surface 56. Thus the cup-shaped end member 42 acts as another electrode of the tube.

The inner planar surfaces 46 and 5@ may be coated with a material h-aving a high electron emission characteristic, such as barium oxide.

The anode is in the form of a fiat annular disc 51 having a diametral leg 53 extending across the center. The leg 53 may be integral with the annular disc 51 or may be a separate rod welded or otherwise secured at its ends to the disc. The disc 51 is secured between the Wall members 38 sand 39 to form a completely enclosed evacuated chamber.

The tube of FIGURE 3 may be utilized in oscillator circuits in substantially the same manner as the tube of FIG- URE 1. For example, the inverted tube arrangement illustrated by FIGURE 3 can be utilized in the circuit shown in FIGURE 3 to operate ars a low frequency oscillator according to` the teaching of the abovementioned copending application. Thus the outer electrodes 40 and 42 are connected respectively across the ends of a high inductance low Q inductor 55, the center tap of which is connected to the anode disc 51. Oscillations can only occur whenI a magnetic field is applied to the tube by suitable magnetic means external to the tube and having pole faces positioned as indicated at 52 and 54 in FIGURE 4. The magnetic field is arranged to pass between the planar surfaces 46 and 5t) and parallel thereto. It has been found that the best operation of the tube as an oscillator is achieved by orienting the field at substantially 45 with rela-tion to the longitudinal axis of the rod anode.

With the arrangement shown in FIGURES 3 and 4, any external heating means may be utilized, since the electron emitting surfaces are in good thermal Contact with the outside of the tube. For example, the whole unit can be placed in an oven or in the vicinity of any heat source. By way of example, a pair of electric heaters are shown as indicated at 53 and 60.

The tube arrangement of FIGURES 3 and 4 can be utilized in the same circuit as described in connection with FIGURE 1. Also it has been found that the circuit of FIGURE 3 can be made to oscillate using the inverted tube structure shown with one of the cathodes iioating or directly connected to the anode. With zero anode potential, the circuit operates in effect as an energy converter in which thermal energy applied to the tube results in a voltage output signal.

What is claimed is:

1, A magnetron tube device comprising a pair of cathode elements having substantially planar electron emitting surfaces in spaced parallel relationship, an anode of an elongated shape extending between the cathode surfaces, the anode having a small surface in relation to` the electron emitting surfaces of the cathode elements, means for heating each of the cathode elements to increase their electron emission, the electron emitting surfaces of the cathodes an-d the anode being positioned Within an evacuated region, and magnetic means for producing a magnetic field with the lines of flux directed between and substantially parallel to the cathode electron emitting surfaces, the flux lines extending at substantially a angle to the longitudinal axis of the anode.

2. A magnetron tube device comprising a pair of cathode elements having substantially planar electron emitting surfaces in spaced parallel relationship, an anode of an elongated shape extending between the cathode surfaces, the anode having a small surface in relation to the electron emitting surfaces of the cathode elements, means for heating each of the cathode elements to increase their electron emission, the electron emitting surfaces of the cathodes and the `anode being positioned within an evacuated region, and magnetic means for producing a magnetic eld with the lines of flux directed between and substantially parallel to the cathode electron emitting surfaces.

3. A magnetron tube device comprising a pair of cathode elements having substantially planar electron emitting surfaces in spaced parallel relationship, an anode of an elongated shape extending between the cathode surfaces, the anode having a small surface in relation to the electron emitting surfaces of the cathode elements, the electron emitting surfaces of the cathodes and the anode being positioned within an evacuated region, and magnetic means for producing a magnetic field with the lines of flux directed between and substantially parallel to the cathode electron emitting surfaces.

References Cited by the Examiner UNITED STATES PATENTS 2,114,114 4/38 Roberts 315-39.71 X 2,163,156 6/39 Samuel 313-158 X 2,166,210 7/39 Fritz 315-3951 X 2,282,856 5/42 Engbert S13-39.53 X 2,607,905 S/52 Ludi 315-3951 DAVID I. GALVIN, Primary Examiner.

ARTHUR GAUSS, JOHN W. HUCKERT, Examiners. 

1. A MAGNETRON TUBE DEVICE COMPRISING A PAIR OF CATHODE ELEMENTS HAVING SUBSTANTIALLY PLANAR ELECTRON EMITTING SURFACES IN SPACED PARALLEL RELATIONSHIP, AN ANODE OF AN ELONGATED SHAPE EXTENDING BETWEEN THE CATHODE SURFACES, THE ANODE HAVING A SMALL SURFACE IN RELATION TO THE ELECTRON EMITTING SURFACES OF THE CATHODE ELEMENTS, MEANS FOR HEATING EACH OF THE CATHODE ELEMENTS TO INCREASE THEIR ELECTRON EMISSION, THE ELECTRON EMITTING SURFACES OF THE CATHODES AND THE ANODE BEING POSITIONED WITHIN AN EVACUATED REGION, AND MAGNETIC MEANS FOR PRODUCING A MAGNETIC FIELD WITH THE LINES OF FLUX DIRECTED BETWEEN AND SUBSTANTIALLY PARALLEL TO THE CATHODE ELECTRON EMITTING SURFACES, THE FLUX LINES EXTENDING AT SUBSTANTIALLY A 45* ANGLE TO THE LONGITUDINAL AXIS OF THE ANODE. 